function p=stdt(x,f1)
% Steepest descent direction;
% INPUT:
%       x - current iterate (n*1);
%       f1 - function handle to compute gradient (Rn->Rn)
% OUTPUT:
%       p - search direction (n*1);
% REVISION:
%       jqin, 15/feb/2011, created;
p=-f1(x);
end